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Fuel Pump Codes 87/95/96 Troubleshooting
Codes Definitions:
87 - Primary Fuel Pump Circuit Failure (CM,O)
95 - Fuel Pump Circuit Open-PCM To Motor Ground (CM,O)
96 - Fuel Pump Circuit Open-Battery To PCM (CM,O)
Fuel Pump Relay & Circuit Description
INERTIA SWITCH
Description:
The ECM generates an initial ground pulse (FP signal at pin 22) to activate fuel pump relay when ignition key is turned on (pump prime). Subsequent FP pulse generation will depend on the presence of the PIP pulse, generated by the stator sensor/TFI module when engine is cranking or on.
The FP signal (FP relay triggering), wire, and relay coil are known as / referred to as the PRIMARY circuit.
At the same time the FP pulse is generated the ECM monitors a 12-vdc signal, from the FP relay, to confirm the fuel pump is receiving power, or its ON/OFF status at pin 19 in the ECM. This signal is identified as the Fuel Pump Monitor (FPM) 12-vdc signal, also identified, or referred to as the SECONDARY circuit.
For the purpose of better understanding the components, codes 87 & 95 are PRIMARY circuit failures and code 96 is a SECONDARY circuit failure code. Code 96 deal with the FPM circuit and codes 87 & 95 with the FP, or triggering signal to activate the FP relay.
Tools Required: (in addition to the generic tools)
Digital VOM or DMM
Wiring diagrams for your year Mustang
Vacuum diagram for your year Mustang
Testing Procedure:
For the purpose of better understanding the components, codes 87 & 95 are PRIMARY circuit failures and code 96 is a SECONDARY circuit failure code. Code 96 deal with the FPM circuit and codes 87 & 95 with the FP, or triggering signal to activate the FP relay.
Codes 87 & 95 (PRIMARY Circuit)Testing Procedure:
1. Code 87 possible causes are:
Open VPWR circuit between the EEC relay and the FP relay.
Open in FP relay coil (faulty FP relay).
Open wire in FP signal circuit (ECM pin 22).
Faulty inertia/fuel-cutoff switch (when inertia switch is part of the primary or "relay activating" circuit).
2. Code 95 possible causes are:
Inertia-fuel cutoff switch is open (when inertia switch is part of the primary or "relay activating" circuit)
Open wire between the FP relay and ECM pin 19 (FPM signal)
Bad FP ground
FP relay stuck closed (FP on all the time even when ignition is off)
FPM signal wire shorted to VPWR
Faulty ECM
3. Verify inertia switch is not tripped or open. Reset if required, if code continues to show, measure resistance at inertia switch pins, if reading is greater than 5 ohms...replace the switch....a no start condition would be obviously present and FP will not prime.
4. Using the supplied diagrams, check for 12-vdc with VOM between the 12-vdc always hot terminal and ground, Ign Off....reading should be 12-vdc....and check for 12-vdc with VOM between the 12-vdc VPWR terminal and ground, Ign On....reading should be 12-vdc....NO….trace and repair open wire, fuse link, ignition switch connector or ignition switch.....YES….goto 6.
5. If FP stays on all the time after turning ign off, locate and remove FP relay...if FP turns off, measure ign on input at relay connector, with ign off, is 12-vdc present.....YES...problem is either a stuck closed EEC relay or the wire is shorted to VPWR....NO...goto 6.
6. Measure for 12-vdc with VOM between the 12-vdc always hot terminal and the FP signal terminal at the FP relay connector, ign off....reading should be 0-vdc....YES....replace FP relay...NO....disconnect ECM, measure resistance between the FP signal terminal at the relay connector and ground...resistance should be equal/greater than 10K ohms...NO...trace and repair FP signal wire short to ground....YES...replace ECM.
Code 96 (SECONDARY Circuit)Testing Procedure:
1. A service code 96 means a fuel pump secondary circuit failure....secondary circuit means the on/off circuit in the relay that supplies the 12-vdc voltage to the pump and is monitored by the Fuel Pump Monitor (FPM) pin or signal at the ECM pin 19.
2. Access ECM connector and check for 12-vdc at pin 19 wire, engine running….reading should be 12-vdc….Yes…replace ECM…NO…trace open wire to FP relay output to fuel pump and repair as required.
3. Clear codes, perform a 5-10 minutes drive cycle, and recheck the system for codes. If codes repeat, an intermittent wiring problem is present or the ECM is faulty.
